Dementia results from a wide variety of distinctive pathological processes. The most common pathological processes causing dementia are AD, cerebral amyloid angiopathy (CM) and prion-mediated diseases (see, e.g., Haan et al., Clin. Neurol. Neurosurg. 1990, 92(4):305-310; Glenner et al., J. Neurol. Sci. 1989, 94:1-28). AD is a progressive, neurodegenerative disorder characterized by memory impairment and cognitive dysfunction. AD affects nearly half of all people past the age of 85, the most rapidly growing portion of the United States population. As such, the number of AD patients in the United States is expected to increase from about 4 million to about 14 million by 2050.
In addition, it has been determined that BACE1 knock-out mice had markedly enhanced clearance of axonal and myelin debris from degenerated fibers, accelerated axonal regeneration, and earlier reinnervation of neuromuscular junctions compared with littermate controls. These data suggest BACE1 inhibition as a therapeutic approach to accelerate regeneration and recovery after peripheral nerve damage. (See Farah et al., J. Neurosci., 2011, 31(15): 5744-5754).
Insulin resistance and impaired glucose homoeostasis are important indicators of Type 2 diabetes and are early risk factors of AD. In particular, there is a higher risk of sporadic AD in patients with Type 2 diabetes and AD patients are more prone to Type 2 diabetes. It is believed that BACE1 levels may play a critical role in glucose and lipid homoeostasis in conditions of chronic nutrient excess. Consequently, the inhibition of BACE1 activity may also be important for the treatment of diabetes and obesity. Specifically, BACE1 inhibitors may be potentially useful for increasing insulin sensitivity in skeletal muscle and liver. (See Meakin et al., Biochem. J. 2012, 441(1):285-96.)
Likewise, inhibition of BACE2 is proposed as a treatment of Type 2 diabetes with the potential to preserve and restore β-cell mass and stimulate insulin secretion in pre-diabetic and diabetic patients. (WO2011/020806). BACE2 is a β-cell enriched protease that regulates pancreatic β cell function and mass and is a close homologue of BACE1. Pharmacological inhibition of BACE2 increases β-cell mass and function, leading to the stabilization of Tmem27. (See Esterhazy et al., Cell Metabolism 2011, 14(3): 365-377). It is therefore an object of the present invention to provide for BACE2 inhibitors that are useful in the treatment and/or prevention of diseases associated with the inhibition of BACE2. (WO2011/020806).
Aminodihydrothiazine or thioamidine compounds are described in WO 2010/038686 as useful inhibitors of the β-secretase enzyme. The invention is directed to novel thioamidine compounds and their use in the treatment of neurodegenerative diseases, including AD, as well as the treatment of diabetes and obesity.